Arenicins are 21-residue cationic antimicrobial peptides, isolated from marine polychaeta Arenicola marina. In order to determine a high-resolution three-dimensional structure of arenicin-2, the recombinant peptide was overexpressed as a fused form in Escherichia coli. Both arenicin isoforms were synthesized using the Fmoc-based solid-phase strategy. Recombinant and synthetic arenicins were purified, and their antimicrobial and spectroscopic properties were analyzed. NMR investigation shows that in water solution arenicin-2 displays a prolonged β-hairpin, formed by two antiparallel β-strands and stabilized by one disulfide and nine hydrogen bonds. A significant right-handed twist in the β-sheet is deprived the peptide surface of amphipathicity. CD spectroscopic analysis indicates that arenicin-2 binds to the SDS and DPC micelles, and conformation of the peptide is significantly changed upon binding. Arenicin strongly binds to anionic lipid (POPE/POPG) vesicles in contrast with zwitterionic (POPC) ones. These results suggest that arenicins are membrane active peptides and point to possible mechanism of their selectivity toward bacterial cells. © 2007 Elsevier Inc. All rights reserved.